1. Field of the Invention
The present invention relates to an image forming apparatus which is implemented by a distributed control system including a plurality of CPUs having a hierarchical structure.
2. Description of the Related Art
In printer device control of an image forming apparatus which adopts an electrophotography system, concentrated control using one CPU is performed. However, a CPU having higher performances is required due to an increase in CPU load owing to the control concentrated on one CPU. Furthermore, along with an increase in load on a printer device, communication cables (communication wiring harnesses) have to run from a control CPU board to distant load driver units, thus requiring a large number of heavyweight control communication wiring harnesses. To solve this problem, a control mode that divides respective control modules, which configure an electrophotography system, into individual sub CPUs has received a lot of attention.
Examples of building control systems by dividing individual partial module control functions using a plurality of CPUs have been proposed in some controlled device product fields other than copying machines. For example, a vehicle system adopts a distributed control system. However, unlike a central administration system based on the concentrated control, the distributed control system requires strict error detection so as to allow a plurality of boards (CPUs), which operate in cooperation with each other, to operate normally.
For example, Japanese Patent Laid-Open No. 2006-191338 has proposed a gateway apparatus, which monitors periodic messages, which are periodically transmitted in a plurality of buses, and detects a faulty device based on communication statuses of the periodic messages. Also, Japanese Patent Laid-Open No. 2002-301997 has proposed a technique for easily specifying failure factors of a vehicle by outputting pseudo-control information from a failure diagnosis apparatus.
However, the aforementioned related arts suffer the following problems. In the distributed control system in which a plurality of CPUs perform cooperative control, it is important to individually make operation confirmations of the CPUs which perform the cooperative control, and to specify a faulty portion when an error has occurred. By providing a device which concentratedly monitors failures, a faulty node can be confirmed. However, a dedicated monitoring node is required, thus causing an increase in cost. When a system is configured to have a hierarchical structure, it becomes difficult to specify detailed faulty portions if failure determination is performed based only on the traffics of upper layers.
It is effective to detect a faulty portion in a test mode. However, when such test mode is applied to an image forming apparatus, the contents to be tested are limited in a state in which a paper jam has occurred due to a failure during operation.
Furthermore, when a dynamic timing error has occurred, or in case of emergency shutdown processing during operation, it is difficult to detect a faulty portion in the test mode.